mass fractions of DL-nornicotine

DL-nornicotine | elemental composition

Find the elemental composition for DL-nornicotine in terms of the atom and mass percents: atom percent = N_i/N_atoms × 100% mass percent = (N_im_i)/m × 100% Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i, m_i, N_atoms and m using these items. • Finally, compute the percents and check the results. Write the chemical formula: C_9H_12N_2 Use the chemical formula to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms, per molecule: | number of atoms C (carbon) | 9 H (hydrogen) | 12 N (nitrogen) | 2 N_atoms = 9 + 12 + 2 = 23 Divide each N_i by N_atoms to calculate atom fractions. Then use the property that atom fractions must sum to one to check the work: | number of atoms | atom fraction C (carbon) | 9 | 9/23 H (hydrogen) | 12 | 12/23 N (nitrogen) | 2 | 2/23 Check: 9/23 + 12/23 + 2/23 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent C (carbon) | 9 | 9/23 × 100% = 39.1% H (hydrogen) | 12 | 12/23 × 100% = 52.2% N (nitrogen) | 2 | 2/23 × 100% = 8.70% Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table: | number of atoms | atom percent | atomic mass/u C (carbon) | 9 | 39.1% | 12.011 H (hydrogen) | 12 | 52.2% | 1.008 N (nitrogen) | 2 | 8.70% | 14.007 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molecular mass, m: | number of atoms | atom percent | atomic mass/u | mass/u C (carbon) | 9 | 39.1% | 12.011 | 9 × 12.011 = 108.099 H (hydrogen) | 12 | 52.2% | 1.008 | 12 × 1.008 = 12.096 N (nitrogen) | 2 | 8.70% | 14.007 | 2 × 14.007 = 28.014 m = 108.099 u + 12.096 u + 28.014 u = 148.209 u Divide the mass for each element by m to calculate mass fractions. Then use the property that mass fractions must sum to one to check the work: | number of atoms | atom percent | mass fraction C (carbon) | 9 | 39.1% | 108.099/148.209 H (hydrogen) | 12 | 52.2% | 12.096/148.209 N (nitrogen) | 2 | 8.70% | 28.014/148.209 Check: 108.099/148.209 + 12.096/148.209 + 28.014/148.209 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent C (carbon) | 9 | 39.1% | 108.099/148.209 × 100% = 72.94% H (hydrogen) | 12 | 52.2% | 12.096/148.209 × 100% = 8.161% N (nitrogen) | 2 | 8.70% | 28.014/148.209 × 100% = 18.90%

Mass fraction pie chart